Hemidirected [M(II)L4]q structures and Jahn-Teller effect

- MP2 geometry optimization of [M(II)L4]q and [M(IV)L4]q−2 complexes, M = Pb, Sn, Ge.
- Holodirected and hemidirected structures.
- Group-theoretical analysis of imaginary vibrations and CIS excited states.
- Pseudo-Jahn-Teller symmetry descent and exceptions.

MP2 calculations of [ML4]q complexes with central atoms M = Pb, Sn or Ge in +II and +IV oxidation states and a series of simple anionic and neutral ligands L, q being the charge of the complex, were performed. Their geometries were optimized in ground singlet spin states within various symmetry groups. Corresponding imaginary vibrations and excited singlet electron states obtained by CIS calculations were analyzed in terms of group theory. The existence of less symmetric hemidirected structures of [M(II)L4]q complexes can be explained by pseudo-Jahn-Teller effect which implies the existence of the structures corresponding to the epikernel or kernel subgroups of the parent groups of holodirected (Td or S4 groups) and hemidirected (C4v or C4 groups) structures. The stability of the high-symmetric holodirected structures of [M(IV)L4]q and some Pb(II) tetrahalides cannot be explained by very high excitation energies only.